I don't pre-wash my fabrics but do starch them before cutting. I use what's we call Quilter's Moonshine which is made with Vodka. I like my starch even heavier so add Sta-Puff liquid starch to my mixture. I rigged up an old top half of a wringer washer that I can stand over my double sink. I pour my starch into a dishpan, soak the fabrics till saturated, then wring the excess thru the wringer. Saves on my hands having to twist and wring the fabric especially those larger pieces. I keep my excess starch in a gallon jug in my fridge I have downstairs. I rigged up a large dowl rod over my sink and hang the fabrics on a hanger to dry. Then once dried, I mist the fabric with plain water ( my steam iron no longer steams) and then press. I made myself one of those big boards...24 x 48 using batting and the silver fabric stapled to the board. Added brackets under neath and lay it over my regular ironing board. Works like a charm for me.
If I feel I need to starch the block later down the road I'll spray it on the backside and press it dry before I attach it to another block and so on.