Iusualy put hose on drain and open up with pressure and let it run awhile 5 Min. If you have big stuff it wont come out, so I turn off El. and drain it down take out element and flush it out best I can and take wet vac and sput 3/4″ hose on vac hose with duck tape and suck out rest, put it all together and wash rest of small stuf out hose bib, by the way make sure water and El. is off before you do work.
Art retired plbg