I hate to tell you this but most if not all of the KR hyper concentrates, those are the products that you mix 10 gallons of water with each 5 gallon pail of
soap product they that made by Simoniz and are all made from the same base and are prone to getting a bacterial growth the tank, this looks kind of like snot, like the stuff that was in your strainer. The strainer should be on the discharge side of your holding tank so this snot doesn’t get into your pumping system, solenoid valves etc. This bacterial growth can be controlled by using a 1 inch swimming pool bleach pellet in your holding tank and frequent cleaning of the holding tank. In the picture of your round holding tank it looks like it needs to be cleaned and the level of the
soap that in tank is too high, our holding tank hold about 3 gallons of foam brush
soap. The KR hyper concentrates have a neutral PH so the cleaning ability off the
soap is just about zero.