Sources say that semi trash pumps usually pass solids 25% of their discharges hose while full pumps can be 50% and higher.
This NorthStar® Full Trash Pump is capable of handling solids up to 1 1/4in., so you can safely use it to pump almost any water, even water with sludge, sand, leaves and twigs.
Semi-Trash Pumps can pass small debris about 5/8 of an inch, like this Northern Tool's 2in. Ports Powerhorse Semi-Trash Pump. The pump housing just isn't large enough to pass larger items.
High pressure pumps on the other hand are most commonly used to pump sludge and extremely abrasive liquids. This makes the pumps perfect for systems where the liquid cannot be completely cleaned by filtration, or where it is just not economical.
High-Pressure pumps also deliver when you need extra pressure to push water across extended distances and heights.
Here's What to Consider when Buying a Trash Pump shared by doityourself.com.