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Old 09-22-2020, 12:27 PM   #1
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Shop Vac Blow down fitting for water lines

Kind of a continuation of the "Why add anti-freeze" thread. I saw a post about using a Shop Vac but no instructions on how to attach to water system.

Parts:
Garden Hose Hex Nipple Nylon - 3/4 MGHT x 3/4 MGHT
shop-Vac® 1-1/4" Wet/Dry Vacuum Extension Wand

I had to remove the 1st half inch of the extension wand to make the nipple fit snuggly, I may glue in place but as of now it is working.


I may start using this to clear the water hose for storage too.
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Old 09-22-2020, 12:29 PM   #2
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Don't use a dirty extension wand
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Old 09-22-2020, 12:52 PM   #3
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Don't know what the psi is for a shop vac, but you need to be careful. If your psi is too high, you could damage the lines. I've read 40psi is recommended.
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Old 09-22-2020, 01:07 PM   #4
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Quote:
Originally Posted by Reverse_snowbird View Post
Don't know what the psi is for a shop vac, but you need to be careful. If your psi is too high, you could damage the lines. I've read 40psi is recommended.
I have know idea about PSI for shop vac, not even sure how I would calculate that. Should be okay as long as there is an open faucet in the bus. That is a good point. I have a pressure gauge for city water I will attach and get back to you.
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Old 09-22-2020, 01:36 PM   #5
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I doubt any shop vac could come close to 40PSI, hold your hand over the end, it should be easy to stop the flow. Vacuums are high volume low pressure. I have no idea if it is enough pressure to do the job but an interesting idea.

My main concern with blowing out the lines is you can never be sure you got the water out of the pump. Or between the pump and your fitting.
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Old 09-22-2020, 01:39 PM   #6
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Shop vac blower would be lucky to make 2-3 psi...it's high volume, low pressure.
Water lines in the RV will be safe.
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Old 09-22-2020, 02:02 PM   #7
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Maybe a better idea would be to use it as a vac, most shop vacs are wet/dry so sucking the water out from the low point drains may be better, still go through and open and close all the fixtures
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Old 09-22-2020, 06:44 PM   #8
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Test drive of blow down fitting works. I attached the shop vac to my 100' foot 5/8'' inch hose attached to sprinkler. The system works and yes the pressure is low, approximately 5 psi. This is a lot slower than using a compressor but it does work. The only comment is the initial back pressure did blow the hose off the shop vac.
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Old 09-22-2020, 07:39 PM   #9
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A friend purchased a used Outback.
First time she turned the water on, water sprayed from the toilet. After replacing a couple of valves, she is replacing the toilet.
The previous owner called himself blowing the water out to winterize. If you don't get EVERY bit of the water out, you get that type of problems.
With rv antifreeze, you don't worry.
This was upstate NY.
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Old 09-22-2020, 08:38 PM   #10
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Originally Posted by jackhartjr View Post
A friend purchased a used Outback.
First time she turned the water on, water sprayed from the toilet. After replacing a couple of valves, she is replacing the toilet.
The previous owner called himself blowing the water out to winterize. If you don't get EVERY bit of the water out, you get that type of problems.
With rv antifreeze, you don't worry.
This was upstate NY.
Totally agree, I have been removing water with air and then filling with the pink stuff ( RV anti freeze) since I started doing this myself. It is about 1 1/2 gals of pink stuff and 10 minutes to fill the lines and make sure any remaining water has a very low freeze point. I live in Norther Indiana, I have had a winter that was -40 for about a week.
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Old 09-22-2020, 08:43 PM   #11
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Quote:
Originally Posted by FTCMCB View Post
Kind of a continuation of the "Why add anti-freeze" thread. I saw a post about using a Shop Vac but no instructions on how to attach to water system.

Parts:
Garden Hose Hex Nipple Nylon - 3/4 MGHT x 3/4 MGHT
shop-Vac® 1-1/4" Wet/Dry Vacuum Extension Wand

I had to remove the 1st half inch of the extension wand to make the nipple fit snuggly, I may glue in place but as of now it is working.


I may start using this to clear the water hose for storage too.
You all do realize that the air coming out of that shopvac is going to contain particles of whatever is inside your shopvac. The filter is going to catch some, but NOT all of it. I've seen dust and such come out of my exhaust on my shopvac....no way in hell am I blowing my water system out with it.
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Old 09-22-2020, 09:58 PM   #12
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Originally Posted by TheWolfPaq82 View Post
You all do realize that the air coming out of that shopvac is going to contain particles of whatever is inside your shopvac. The filter is going to catch some, but NOT all of it. I've seen dust and such come out of my exhaust on my shopvac....no way in hell am I blowing my water system out with it.
Totally agree.


If I lived in the north, I would use anti-freeze. Living here in the south, I use an air compressor to blow out the lines. It drops below freezing, some times days in a row, but during the day it nearly 100% of the time well above freezing, so just blowing the lines works for me.


But with a shop vac? Naw, ain't happening.



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Old 09-23-2020, 01:20 PM   #13
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Blow It Out/Then Use Antifreeze

Doesn't take long, blow it out then use the pink stuff. -40 is NOT unusual up here in Canada.
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Old 09-23-2020, 01:45 PM   #14
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I'm the guy who posted that I use a shop vac...so I'll try to respond to some of the opinions/concerns. I'll attach a picture of the basic adaptor to the hose fitting but the fitting to connect to the piping network is in the trailer in storage. It's pretty simple, available anywhere.

Good point about the risk of blowing dust and junk out of the vac, but I start with an empty (still a bit dusty in there) vac canister and turn it on for a minute before connecting it to the trailer...blow it into your face for a second while you bang on the canister if you want to check how good or bad it is (it's not bad).

I think it's better to blow air through than suck water out. I check for good airflow and no water drops coming out of each fixture to be sure the lines are clear.

I first unscrew the inlet filter bowl, dump the tiny bit of water in the bowl, connect to the city water inlet (standard hose fitting) and blow out piping to the bowl. I screw the bowl back on and blow through the pump. This is the part that some might think is risky, possibly damaging the pump or flow control valves. Maybe - I've never had a problem and, as has been said, the static pressure is pretty low out of the shop vac. I've added a T fitting at the outlet of my water tank so I can also blow air through that hose up to the pump. I use an adaptor from the hose fitting to a fitting on the pipe I've taken off the pump, to blow air from pump to the fittings around the trailer.

This is definitely one of things we all have opinions about...all I can say it's worked well for me so far.
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Old 09-23-2020, 01:51 PM   #15
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i think it's a bad idea all the way around . if your going to use air then use air get a small compressor . doesn't have to be big one,a small 3 gallon compressor will be just fine . if not forget the shop vac just pump antifreeze through and push the water out . no big deal and you don't uns anymore antifreeze
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Old 09-23-2020, 02:03 PM   #16
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I agree with Mr. M. We know an air compressor works well to blow out the water lines set to 40psi so why reinvent the wheel and give yourself more questions than answers about dirt contamination, ultimate PSI, etc.

Maybe your shop vac is bigger or smaller than jackconn's, so will it work as well? Who knows?

Get a small air compressor and set it to 40psi or just buy one of those portable air tanks with a hose, fill it to about 45 psi and use that. They sell the small air hose fitting that screws into your fresh water fill hose port at any hardware store, Lowes or Home Depot. My air compressor allows you to set the air resevoir to any pressure so I can set it to 45psi, shut it off and use it with the correct pressure. Easy peasy. A 12v. or 110 v. air compressor is a good investment if you don't have one.

I'm a little nutty over having air with me, so I even have a 200 psi compressor with a three gallon holding resevoir installed on my Dodge RAM 3500 tow vechicle. I can air up my tires while in the boondocks if needed. (I also have a four-trumpet train horn installed ... did I say I was a little nutty over having air on board?)

Just use an air compressor. Don't make your life hard.
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Old 09-23-2020, 02:11 PM   #17
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Originally Posted by walaby View Post
Totally agree.


If I lived in the north, I would use anti-freeze. Living here in the south, I use an air compressor to blow out the lines. It drops below freezing, some times days in a row, but during the day it nearly 100% of the time well above freezing, so just blowing the lines works for me.


But with a shop vac? Naw, ain't happening.



Mike
Never did the Air thing. Always just pumped the Pink thru the system and was done. Lots of below Zero in Nebraska too.
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Old 09-23-2020, 04:26 PM   #18
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Quote:
Originally Posted by FTCMCB View Post
Kind of a continuation of the "Why add anti-freeze" thread. I saw a post about using a Shop Vac but no instructions on how to attach to water system.

Parts:
Garden Hose Hex Nipple Nylon - 3/4 MGHT x 3/4 MGHT
shop-Vac® 1-1/4" Wet/Dry Vacuum Extension Wand

I had to remove the 1st half inch of the extension wand to make the nipple fit snuggly, I may glue in place but as of now it is working.


I may start using this to clear the water hose for storage too.

Just use the antifreeze and know that without a doubt that your trailer is secure and that there will be no surprises in the spring.



Also, do you ever worry about what can grow in an empty water line?


Antifreeze insures there is no place for bacteria to grow.


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Old 09-23-2020, 04:49 PM   #19
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This isn't a blow out vs antifreeze thread. That subject has been beat to death.
This is about blowing your system out with a shop vac.
Personally, I wouldn't do it as it seems a bigger PITA and slower than using an air compressor. And what RVer doesn't at least carry a small air compressor with them at all times anyway?
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Old 09-23-2020, 05:30 PM   #20
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Thoughts:

First...thanks for the idea. What's to come here does not diminish the value of you sharing something clever.

A Shop Vac is not a "pressure" machine. It's a volume pump...like a beach toy inflator. It's not really up to the job of blowing water out of the lines. Don't believe it? Put your hand over the vac's "exhaust." It takes little effort to hold your hand there. Now take your compressor and the adapter described below and feel the difference in force.

An air compressor, especially a fairly big one, is the right tool for the job. I have this one, and it does the job with ease: https://www.homedepot.com/p/Husky-30...303H/206532808 As compressors go, it ain't much, but it's more than up to this task and any other jobs related to RV-ing. I set the output pressure to 40 PSI, and there is no danger of damaging the plumbing. A variety of simple adapters make the connection to the city water hookup easy: https://www.amazon.com/Hotop-Winteri...9WN4ADEJNF45SV I made my own with a conventional NPT male air quick connect and a 3/4" to 1/2" adapter from Home Depot...cost half that much.

I used a pancake compressor for years, but I had to let it recharge 4 to 6 times, because it could not deliver the CFM required to do the job in one "blow." Which brings us back to the Shop Vac...not a chance.

Not to mention that a shop vac is filthy if it has EVER been used. The entire interior, the filter, and the hoses are dirty to say the least. And ALL the air has to flow through the entire vacuum cleaner before exiting the exhaust. Your compressor, on the other hand, inhales filtered air, has never been contaminated with dirt, and the hoses are all blown clean and dry with each use. The only contaminants would be water, and you're supposed to use the drain petcock to deal with water in the pressure tank.

As for garden hoses...freshwater, grey water, and so on, the easiest way to drain them is to lay them on a slope. In the case of the freshwater hose, place each end on a clean plate or piece of cardboard to keep the hose end off the ground. Gravity will do the rest far more quickly than trying to blow them out with any kind of air pressure. As a P.S. on this, I always pre-treat my freshwater connections, from the hydrant to the gravity fill (in my case) with a product called Clorox Cleanup (or generic equivalent). I spray all connections and fittings and let them sit for about 15 minutes to let the chlorine do its job. Then, before adding water to the fresh tank...or using the city water, I flush out the cleanser with a few gallons of water.

Using a Shop Vac as a "blower" does have value in many applications. I was a hobby cabinet maker for many years, and sawdust is the enemy...a fire hazard at minimum. I used my Shop Vac's exhaust to blow dust out of inaccessible places lots of time. That adapter would have allowed me to add a short length of garden hose to reach into the tight spots, and to reduce the volume of air by a factor of about 3 or 4 for delicate jobs. But I would never use it on a potable water system.
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