Y'all have already said just about everything I'd say, but I do have a couple of comments and questions, starting with:
Who installed this system???
Why does the pumpout hose come all the way back to the head (can't tell where it goes from there)? It should go straight up (at least as straight as possible) to the deck pumpout.
The route TO the tank should go up immediately after the toilet and then to to the tank.
If both of those are impossible, is there any chance you can relocate the tank, even if it has to mean replacing it?
Trident 101/102 sanitation hose is an excellent choice UNLESS there are more than a couple of bends in the route that are tighter the hose wants to bend willingly...'cuz it's so stiff that you'd have to cut it and install inline radius fittings. Raritan SaniFlex hose is proving to be equally as resistant to odor permeation as 101/102, and has the added advantage of being so flexible it can bend as tight as a hairpin without kinking.
just installed a new head and used flexible PVC. Somewhere I read that it was good for sanitation hose. Our RV has PVC so I was thinking that is OK. Sure hope I did not make a mistake.
You're not gonna like my answer....
Boats aren't RVs...RV tanks hang outside under the coach and most RV toilets are "direct drop" into the tank--but any hose from one that isn't is outside under the coach too...so there isn't any sanitation plumbing inside the coach, nor any holes in the floor that are under water. You can get away with almost any hose on an RV. But the entire sanitation system on a boat is INSIDE the boat, with hoses going to the tank and from it to a pumpout fitting and/or plumbing to dump the tank at sea.
Flex pvc #148, which is available from marine stores, is the least expensive sanitation hose...ok for tank vent lines and toilet intake lines, but not the best choice for toilet and tank discharge because it can permeate with odor very quickly...or not. It had been on one of my own boats for 7 years without a trace of odor when I sold the boat...on the next boat it permeated in less than 90 days (took me another month to find the source of the odor 'cuz I couldn't believe it could be brand new hose and so I refused to test the hose for it). So if that's what you used, you may or may not get lucky.
But if you went with spa hose from a big box hardware store, you made a big mistake 'cuz although it may look exactly like #148, it's not the same hose. Not only will it start to stink very quickly because it's WATER hose, not rated to carry carry sewage...nor is it rated for use on below-waterline connections--iow, any tank overboard discharge plumbing.
Sanitation hose is one thing on a boat where it doesn't pay to go cheap....Trident 101/102 and Raritan SaniFlex are a lot more expensive than flex pvc, but worth the price if you only want to have to do that miserable job once.