You can't blow out your holding tank. There should be a drain hose with a screw on plug at the bottom of your RV to drain it. Also, don't put any antifreeze (RV type) in your holding tank. Be careful how much air pressure you use when you blow out your lines. Check around but I believe you don't want to exceed 45 psi or so. But don't go in there with 100 psi or you could blow things to smitherines! Lots of people use pressure limiters on city water to avoid this problem.
2012 F150 FX4 Ecoboost, 2016 Surveyor 274BHS
2003 Yamaha FJR1300, Demco Premiere Slider
1969 John Deere 1020, 1940 Ford 9N, 1948 Ford 8N
Jonsered 535, Can of WD-40, Duct Tape
Red Green coffee mugs