Beginner’s Guide To DIY Greywater Check Valves There are two types of check valves; spring and gravity flow.Spring valves are used in pressurized systems.Since greywater systems are usually gravity flow they use the gravity flow check valves. You Might Also Like Beginner’s Guide To Greywater 3 Way Valves Part 1 April 26, 2020 Beginner’s Guide To The Aquifer Coupler April 26, 2020 Beginner’s Guide To Aquifer Expanded | 3 main functions April 26, 2020