Black tank chemical mix when winterizing

[Cracker]

In all the years I’ve been doing this I’ve never worried about anti-freeze mixing with Thetford holding tank additive - but is it a no-no? My new-to-me Cougar came with a great little spray wand, with a rotating head and jet nozzles for the black tank, that you use by simply inserting it into the open toilet and turning the water on. I had dumped the tank when we left the last campsite a couple of weeks ago, after which I had faithfully added the Thetford additive to the tank. That said, I decided to use the little spray gadget today and give the tank a thorough cleaning for the winter. Well, after taking six 5-gal pails to the brush pile, the water was running about as clear as dishwater and I called it quits. I also blew out the water lines with my compressor and drained the fresh water tank and water heater - so all that remains is to pump anti-freeze through the system using the onboard pump. That’ll put a couple of quarts of anti-freeze in the black tank, using my normal procedure, and I simply started wandering if I should add another 8 oz of the Thetford additive to prevent odors. In the past I haven’t gone thru the thorough cleaning procedure for the black tank, simply letting the anti-freeze mix with the Thetford additive. Being retired, I’ve got too much time to think about these things!!!

The other thing I found to be questionable is that the tank drain on this unit hangs down about 4 inches below the tank, terminating in a screw-on cap to facilitate draining. My last unit had a valve on the side of the tank. When I unscrewed the cap to drain the tank it continued to drip after the tank was virtually dry. Even if I left it open overnight I’m sure that it would still drip from condensation in the tank, etc. If so, the 4 inch protrusion will fill with water if you cap it and, thanks to our -20 deg temps here in Maine, it will probably freeze and crack. If you leave the cap off, the mud-daubers will get to it in the spring if the mice don’t squeeze in during the winter. My solution was to cut a 4” length of “pool noodle,” stuff one end full of a fabric-softener sheet, and slip the other end over the end of the drain pipe - leaving the cap off till spring.

[66joej]

In all the years I’ve been doing this I’ve never worried about anti-freeze mixing with Thetford holding tank additive - but is it a no-no? My new-to-me Cougar came with a great little spray wand, with a rotating head and jet nozzles for the black tank, that you use by simply inserting it into the open toilet and turning the water on. I had dumped the tank when we left the last campsite a couple of weeks ago, after which I had faithfully added the Thetford additive to the tank. That said, I decided to use the little spray gadget today and give the tank a thorough cleaning for the winter. Well, after taking six 5-gal pails to the brush pile, the water was running about as clear as dishwater and I called it quits. I also blew out the water lines with my compressor and drained the fresh water tank and water heater - so all that remains is to pump anti-freeze through the system using the onboard pump. That’ll put a couple of quarts of anti-freeze in the black tank, using my normal procedure, and I simply started wandering if I should add another 8 oz of the Thetford additive to prevent odors. In the past I haven’t gone thru the thorough cleaning procedure for the black tank, simply letting the anti-freeze mix with the Thetford additive. Being retired, I’ve got too much time to think about these things!!!

The other thing I found to be questionable is that the tank drain on this unit hangs down about 4 inches below the tank, terminating in a screw-on cap to facilitate draining. My last unit had a valve on the side of the tank. When I unscrewed the cap to drain the tank it continued to drip after the tank was virtually dry. Even if I left it open overnight I’m sure that it would still drip from condensation in the tank, etc. If so, the 4 inch protrusion will fill with water if you cap it and, thanks to our -20 deg temps here in Maine, it will probably freeze and crack. If you leave the cap off, the mud-daubers will get to it in the spring if the mice don’t squeeze in during the winter. My solution was to cut a 4” length of “pool noodle,” stuff one end full of a fabric-softener sheet, and slip the other end over the end of the drain pipe - leaving the cap off till spring.

Why not put a 1/4 turn plastic valve on the drain. The water will expand up into the tank if it freezes so should be OK. We live in the Frozen North as per my sig. and never had a problem with a small amount of water left in the tanks.

[travelin texans]

If you've drained/flushed the tanks thourghly & added anti freeze down the drains, I wouldn't add the deodorizer, should be very little if anything in there to stink.
If you're worried about the valves freezing, drain what little runs out after you've parked it & leave the valves open.

[DocP]

In 40+ years of camping, I've never added any more chemicals to the black tank after winterizing, and have not had a problem with bad smells in the spring.

[JRTJH]

I live in the "tundra" in northern Michigan, regularly get -20F temps for weeks on end. I flush and drain the tanks as a part of winterization. Run antifreeze through the hot/cold lines, then park the trailer in our pole barn. Once parked, I open all the faucets, put a 5 gallon bucket under the dump opening and open all the valves. After a couple of days, I remove the bucket as there's nothing else to drip out. I leave the valves open, that way if anything should still be in the tanks, even if it migrates to the valves, it can't freeze and expand.

Come spring, I drag the trailer out of the pole barn let it sit in the sun for a day or two, then close the valves, flush the antifreeze out of the lines, sanitize the fresh water system, check everything for leaks and we head north to do some fishing.