Your search for "water flow parts" revealed the following:

Stainless steel pipe 0.7mm OD 0.5mm ID 0.5mm : Sakatsu Material Non-scale 4653

Stainless steel pipe 0.6 mm OD 0.4 mm ID : Sakatsu Material non-scale 4652

Fog generator module option water supply wick (3 pcs.) : BitTradeOne Material Non-scale MMSTGN-OP1

Stainless steel pipe, outer diameter 2.0mm, inner diameter 1.7mm : Sakatsu material, Non-scale 4659

Hexagon Socket Head Fittings, 1.2mm Flat, Tapered : Sakatsu Detail Up Non-scale 4463

Hexagon Socket Head Fittings Double 1.5mm dia. with Taper : Sakatsu Detail Up Non-scale 4460

Introductory Material Set: River and Waterfall - Woodland Material - Non-scale LK955

Hexagon Socket Head Fittings Double 1.2mm Flat, Tapered : Sakatsu Detail Up Non-scale 4462

Hexagon Socket Head Fittings, Double Dia. 1.8mm Flat, Tapered : Sakatsu Detail Up Non-scale 4458

Bugbear Chieftain : HERMIT INN Unpainted Kit Non-scale HM007

Brass pipe outer diameter 1.5mm inner diameter 1.2mm : Sakatsu Material Non-scale 4635

Hexagon Socket Head Fittings, Flat 1.5mm Dia. with Taper : Sakatsu Detail Up Non-scale 4461

Hexagon Socket Head Fittings, 1.8mm Flat, Tapered : Sakatsu Detail Up Non-scale 4459

Stainless steel pipe 0.9mm OD 0.7mm ID : Sakatsu Material Non-scale 4655

Stainless steel pipe, outer diameter 0.5 mm, inner diameter 0.3 mm : Sakatsu material, non-scale 4651

Stainless steel pipe, outer diameter 1.2 mm, inner diameter 1.0 mm : Sakatsu Material non-scale 4657

Hexagonal pipe joint, double flat 1.8mm : Sakatsu Detail Up Non-scale 4450

Rail joiner for code 65, 24 pcs: Atlas Kit N (1:160) 2490

Code Outer diameter approx. 1.2 mm Red colour : Sakatsu Material Non-scale 4518

Hexagonal pipe joint, double flat 1.5mm : Sakatsu Detail Up Non-scale 4452