I leave mine in all season and buy new ones when in the spring. I could clean them for the new season but life's too short.

Laszlo

   Not to "beat a dead horse" but I always weigh my epoxy - always acccurate and no new pumps to buy or clean

   Fine to leave the pumps in place for a season, wipe the tip with a clean paper towel if you notice any crust (which won't be evident for many weeks - longer than most single builds take).

To lash the dead horse just a bit, and because life is short, whenever I'm mixing more than a few ounces I just pour into separate, labeled graduated measuring cups straight from the jug, then pour those together into a mix cup.  Thus measured by volume, not weight.  I use separate, labeled (popsicle) sticks to scrape the A and B cups mostly clean into the mix cup.  These measuring cups and scraper sticks can be used many, many times over, then either replaced or wiped clean for further use. For the bigger batches this has always worked fine for me (ever had a non-hardening batch) and saves a lot of pumping time, and brain-work keeping pump-stroke counts straight.  You can even hold the pump pick-up straw over the measuring cup, catching those drips while pouring, then put the pump right back into the top of the jug.

 Yes, you need to clean the pumps and re-cap the jugs of epoxy and hardener at the end of each day because epoxy and hardener can start to cure in the pumps if left in contact for extended periods, potentially leading to clogs. Cleaning them helps maintain functionality. Leaving the jugs open can allow moisture and air to enter, which may affect the quality of the epoxy and hardener over time. Dust and debris can settle in the open containers, leading to contamination of your materials. @ geometry dash lite