We have $20k, which used fiver under 29' that can dry camp?

Not a good idea to dump directly into the park sewer. The waste still goes through the tanks, the liquid will drain off but leave the solids behind creating the dreaded 'pile'. Best to let the black tank fill at least 3/4 full to allow the waste to soften and partially decompose. You can hook the water directly from the cg bib but it would be wise to use a hose designed for potable water along with a regulator at the bib. Depending on the water source you may also want a filter.