I use Super Clean by Castrol. It is a degreaser and can be diluted or used full stregnth for stubborn stains. You can usually purchase it at an automotive shop and sometimes WalMart. It has worked great on tree sap, bird deposits and everything. That is what my dealer recommended and I have been using it for 3 years now and am happy with the results. Others also use a product called Osso which can be found online. Hope this helps.
1 30 yr old Army, back on US Soil, 1 15 yr old DD
'14 Ram 2500 Mega Cab Diesel 4 X 4
'14 Jayco Eagle 298RLDs