After winterizing, I still have standing water beside the toilet.
by winterizing , what do you mean ?
did you drain all the system and replaced with antifreeze ? or blown all the water out ?
If so , the water fund may be from leaking roof vent .....
give it close look
1996 C-21 Triple E ..... 86 Jeep CJ quite modded , 84 olds cutlass resto mod ,
On or off road , I`m on the road ! roadtrips !