Thank you for your question. I am sorry about the confusion and I will be happy to help. The "TP" in the 561-TP-DST stands for "tract pack" which means that it comes with a set of three 561-MPU-DST's. The "LPU" stands for less pop-up, meaning this unit does not come with a pop-up assemby. The "GPM" stands for gallons per minute (US flow rate), this unit has a lower flow rate of 1.0 GPM. There is no difference other than this.
Date published: 2019-10-03