Yes, We have helped others with the seasonal camper clogged black tank problem using the RV-Digest-It from www.rv-digest-it.com
Follow the directions for the "24 hours" soak.
One quart in the tank and wait 24 hours.
Then dump and flush with a toilet wand.
Repeat after 72 hours.
The flush is easier to do if you have a clear elbow on your dump mast.
Plan on doing this at least twice; so think ahead when you order from them. You will be using it occasionally from now on to keep that squeaky clean tank... well... squeaky clean.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW