Prep the suet: Cut your pieces of suet into small cubes. Discard any impurities or pieces of meat that may still be attached to the suet.
Add all your cut up fat trimmings into a large pot.
Pour filtered water over the suet. The amount depends on the amount of fat you're rendering, as well as the size of the pot. The water level should come up about 1/4 of the way up in the pot.
Add about 2tbs of salt, and mix everything thoroughly.
Bring to a simmer, then turn heat down. You want the mixture to be hot and simmering lightly, but not actively boiling.
Leave on light simmer for 4-8hours, until most of the fat melts.
Extract any unmelted chunks with a slotted spoon. Then, pour the tallow into a metal strainer lined with a cheese cloth, on top of a large metal bowl.
Allow to strain through. Then, cover the metal bowl with plastic wrap and set it the fridge to harden up, for about 5 hours.
When hard, press on the sides of the metal bowl and the top layer of rendered tallow will pop up in a single piece. Discard any water & impurities left below.
Add tallow to a large pot, cover with filtered water and repeat the entire process again for second rendering.
Once done, your tallow should be white and odorless. If not, repeat the process one more time.
Place in an airtight container or ziplock bags until you're ready to use the tallow for cooking or other DIY projects.