Amenment to previous reponse...
If there's a vented loop in the head discharge immediately after the toilet, any water in the discharge hose between the toilet and the top of the loop will run back down unless you use "dry bowl" long enough to push it all over the top--and a some may still remain. So if the joker valve is leaking, it will come back into the bowl...but it should only be clean flush water (unless you haven't been flushing enough to rinse the hose out)...you shouldn't feel ANY back pressure when you flush...and it should only seep, it should NOT gurgle and spit. If it does, you have a problem somewhere downstream that needs to be corrected in addition to replacing the joker valve.