Micro PVC – 6mm OD x 4mm ID – Sold by the meter – GrowInsane
Nylon 4MM OD Green 100 ft | Polyconn
High Temp Silicone Tubing Rubber Plastic Tube Hose For Pump Transfer - Temu
Reinforced EPDM Tubing - 4mm ID x 9mm OD x 5 ft. Long
MECCANIXITY Clear Rigid Tubing 4mm(5/32'') ID x 5mm(3/16'') OD x 305mm/12inch Plastic Water Tube for DIY, Pack of 2: Amazon.com: Industrial & Scientific
Plastic Pipe Rigid Tube Clear 0.16"(4mm) ID 0.2"(5mm) OD 6" (150mm), 3pcs - Bed Bath & Beyond - 36760106