When we are staying for over a week on a campground site without sewer, we always move our coach to dump our tanks and chose never to use a "pump-out" truck.
Often times pump-out hoses use Valtera / Thetford sewer connections and suck out tank contents, relying on coach's roof vent pipe to let air into tank as contents are removed. Anytime we dump, tank walls can be flexed if vent pipe does not let air in as fast as tank is emptied. And suction removal increases the chance of wall flexing. Having the toilet valve completely open helps a lot to not stress black tank when dumping. Pump out often sucks water out of sink p-traps, indicating vent pipe cannot keep up.
Maybe over time, holding tanks could fail from too many pump-outs and certainly one overly aggressive pump-out will damage tank. We also feel it does not hurt to start our engine and move about if we need to dump. When we are staying a few months at a full hook up site, we batten down the insides and take our coach for highway drive once a month. We also make an effort to back up several times to keep brakes from setting in one direction.
I have not used a pump truck but used a pump all the time on my sail boat with no ill effects over 20 years. It depends on the truck. I open would open up the toilet with the stopcock but the grey tank is a bit harder to do that
We have used pump trucks at Nascar events for years with never a problem. These guys use a 2 inch diam. x 2 ft long pipe with a valve on it connected to their vacuum pump. They stick the pipe into your flex hose and when you open your dump valve, they open their valve and suck out the contents. The key thing here is that they do not make a tight seal to your holding tank so you never draw any vacuum on your holding tank. The difference in the diameters allow air to be drawn in at the end of your hose If they want to use and adapter and hard connect to your hose, say thanks but no thanks.
Hi All,
When dry camped at the EAA Fly-in, we have had our tanks pumped numerous times. The pump man would always empty our tank into a five gallon bucket, and at the same time, he pumped the bucket contents to his trucks tank. Always worked well.
Raymond
Raymond, you have found the very best way to dump tanks... Dump into a Rubbermaid container or bucket while the container is being pumped out. Pumping out this way supports my comments on how direct connection to pump-out can damage tank.
Any pump-out that does not use direct connection will be safe. But we should all fully open toilet when dumping black tank let air quickly enter tank, which assumes the toilet can have open air flow into tank.
By the way, we planned on doing Oshkosh Fly-In when we left Cleveland Ohio last month, but at the last minute decided to go the other direction to New York City this year.