Here is something most printers don’t think about: the washout is a gentle process as the emulsion is in its most tender state. No pressure washer or forceful water pressure is needed UNLESS you over exposed. Liberally wet both sides of the screen using a garden hose with an adjustable nozzle.
One that has several settings works well (i.e. shower, jet, fan and mist). After getting it wet completely, let it soak for 30 seconds.
Using a soft soaking spray you’ll rinse both sides again then start your final wash from the SHIRT side, as this is the side that received the most light and is stronger. If needed use the flat or fan setting on the nozzle and wash side to side until everything is cleared out, then use the shower setting to give a final rinse all over. If you do need to use more pressure, use a wide fan spray and yes, a pressure washer is acceptable.
But again set the nozzle at a fan setting and use only at a distance, one to two feet, on the shirt (flat) side of the screen.
After you’re satisfied with the results, arrange some old newspapers and lay your screen flat on top of them. Lay one sheet on the inside and SMOOTH it out over the inside quickly and semi firmly but DO NOT RUB. This will ensure you remove the water from the image and will allow you to go to your next step quicker.