Black Tank - How empty is empty?

[Skip12]

Hey all. Trying to help my next door camper. He's convinced his black tank is blocked because there is about an inch of water at the bottom after emptying.

I told him that after 2 nights with 2 adults + 2 kids then emptying results in 1 inch of black water, you're probably fine. Next week, we'll meet out there without the kids, fill it up and dump it, but he's really nervous about filling it up and then not being able to dump anything right before the cold weather rolls in.

In your experience, how much water can be left over in the black tank after dumping?

For me, I've never considered it because we always refill with a few gallons immediate after dumping except when winterizing.

Thanks for any advice or experience you can share.

[bedubya]

Originally Posted by Skip12

Hey all. Trying to help my next door camper. He's convinced his black tank is blocked because there is about an inch of water at the bottom after emptying.

I told him that after 2 nights with 2 adults + 2 kids then emptying results in 1 inch of black water, you're probably fine. Next week, we'll meet out there without the kids, fill it up and dump it, but he's really nervous about filling it up and then not being able to dump anything right before the cold weather rolls in.

In your experience, how much water can be left over in the black tank after dumping?

For me, I've never considered it because we always refill with a few gallons immediate after dumping except when winterizing.

Thanks for any advice or experience you can share.

You're right. It's not a problem. In most tanks, the drain isn't at the absolute bottom. If he's really concerned, he could raise the curbside (with blocks or levelers) when draining for winter, in order to get more water out. But an inch of water in a 7 inch high tank will not cause a problem even in a hard freeze. The water will expand upward just as it does in an ice cube tray. It will NOT break anything.

[NavyLCDR]

Sounds normal to me. 1" of water left in the tank cannot be due to a complete drain blockage because the standard black water tank drain is, I believe, 3" in diameter.

If really worried about residual water freezing in the tank, just pour a gallon of antifreeze down the toilet.