larger spray rigs normally have some sort of "agitation" setup.. basiclly it sucks fluid from tank, and then pumps it right back into the tank to mix it all up.
pending on spray rig you have, you could possibly easily DIY an agitation setup.
they make a rubber "bulkhead" they give it a special term / name that. i do not remember right off. ya drill a hole through the plastic container, that is a little smaller than the bulkhead, and then shove a pvc pipe in. (with some dish soap or like) and the pipe cause the rubber bulkhead to expand and squish into the hole ya drilled to create a nice water tight seal. nice thing about the rubber bulkhead is it allows you to get a bulkhead through round containers, were there really is no flat space, to get a regular bulkhead to work and get a good seal.
a DIY spray bar = a pvc pipe. with some small size holes drilled in it. kinda mimics a lawn sprinkler, but not as small of holes or as many of holes. you most likely will want 2 rows of small holes. a "drill press" and some sort of make shift "V notch" in say a 2x4. to hold pipe as ya drill the holes.
for above spray bar. you most likely will need to drill 2 holes in your tank, and have 2 of the rubber bulkheads. and push a pipe all the way through container. getting the "spray bar holes" some place inside your tank. add a end cap to one end of this pvc pipe. and connect a hose and valve to other end. and hook into current plumbing coming off the pump.
if you place the spray bar correctly in tank, you can use it, to help wash out the tank / flush out the tank. if you are wanting to clean it out and use a different chemical. beyond simple agitation / mixing of the water/chemicals.
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pending on type of pump you have, you might be able to temporarily remove the pre-filter. while you mix water/chemicals via agitation setup.
