Here's a cheap method:
1. Use a large plastic garbage can (30 gal). & pour in rocks
2. fill with water & 1 qt. flushing agent (Flora Kleen, Final Flush, etc...), let sit 12 hours
3. buy a cheap water pond pump at Wally World or Home Depot ($15)
buy 8 feet of 3/4 in. plastic hose & clamp (check size output of pump, it maybe 5/8")
4. place pump in bottom of garbage can & pump out water & stuff
5. After emptying garbage can, I fill w/water hose & continue to pump out, but you need to control the water input so you don't over flow. Pump for 15 - 20 minutes. Works great.

Good Luck, PIF