Clean and lube the toilet bowl seal
Turn off water to RV
Open/Hold Open toilet flush ball
Then Using your hand/fingers rub/flex the bowl seal o remove any crud
Then soap up and thoroughly clean the seal & ball
RInse with a bottle of water to remove soap
Pat dry with paper towels then lube the seal (olive oil works GREAT) using you hand/fingers....all over the seal and ball
Open/Close Ball the check that it fully closes
Turn water back on and flush toilet.
Then water should stay in bowl
If it still leaks you can REPLACE the seal vs new toilet
Course that would require Brand/Model of toilet to get correct parts
With flush pedal on Left side you probably have a Sealand/Dometic Toilet ---- 2000 series, 900 series or Traveler Lite model
Look at the Chart in Link to ID which toilet is yours (I'm guessing Traveler)
That sprayer is FOR Cleaning the bowl....it has FULL water pressure when you FLUSH the Toilet and hold pedal down
FULL Water Pressure......