Nicoll, Male-female inspection pad + plug, grey PVC, Ø 100 mm, allows easy access to pipes, connections made of smooth, non-microporous PVC - prevents impurities : Amazon.com.be: Garden
Amazon.com: PVC Bulkhead Fitting Water Tank Connector Adapter Fitting with Plugs for Rain Barrels, Water Tank, Aquariums and Ponds (1.5"-1pcs) : Industrial & Scientific