true, and also the reason that most of us don't keep our drains open is because the TOILET in the RV usually does not have a 'p-trap' to keep sewer smells from the sewer system from coming up into the RV.
Now, a way around this, if you DO want to keep your drains open, is to have a 'p-trap' as part of the permanent PVC piping from the RV to the sewer drain outlet.
As for the piping part, pvc is easy to work with, easy to cut, and different types of connectors are easily found. A connection to your existing Main outlet might be harder to find, but you could also make one yourself...diy.
An easier route, though, is to just invest in a decently 'thick' RV Sewer Hose and use it. It is well designed to easily handle your needs, even for the long term.
'14 Thor Palazzo 33.3 compact diesel
KingTailgater2 Dish, 100w/5amps roof SOLAR, BlueOx, 100,000+mi since '14... US, Alaska, and Canada... from GA, then NC, now N AL : )