My son-in-law has a Salem trailer. The 3"pipe from toilet to tank looks like it goes to about 2" from bottom on tank. Therefore the toilet solids will not flow out in the tank. I think the pipe needs ...
The RVs I've had have always been like that. I think the idea is that helps the extra water you SHOULD be using disperse the solids when you flush instead of just washing over the pile to the sides of the tank. Should not be a problem if you always dump an extra bowl or two of water after a flush. There is probably a dried up partial "poop pyramid" stuck to the bottom of the tank making for a difficult flush.