I made a test tube holder out of LEGO pieces. It's stackable, you can build more stories on top of each other. It's pretty portable in its current state and really sturdy. :
LEGO® Creator 10257 Carousel | New Elementary: LEGO® parts, sets and techniques
MOC Technical Parts Connectors 40pcs TUBE W/DOUBLE DIA4.85 Compatible With Lego Building Block Bricks Bulk for Kids Toy 62462 - AliExpress
LEGO+Technic+6173127-+62462+Tube+W%2F+Double+4.85+Hole+Medium+Stone+Grey+X2 for sale online | eBay
Bricker - Part LEGO - x153 Aero Tube 32 x 3 x 2 1/3
Lego Tube In Lego Bricks & Building Pieces for sale | eBay
Amazon.com: LEGO Tubes Experiment DUPLO Set 9076, Fun STEM Educational Toy, STEAM Learning for Girls and Boys Ages 1.5 and up (142 Pieces) : Toys & Games
LEGO Flexible Ribbed Hose (19 Studs Long) with 8 mm ends (14925 / 57539) | Brick Owl - LEGO Marketplace
Help to identify a small tube part - Bricks
LEGO® Technic Pneumatics T-Bar / T-Peace / Tube Connector MEDIUM STONE GRAY (MED. ST. GRAY) - (
LEGO elemento 73590c01a - Black Hose, Flexible 8.5L with Tabless Ends (Ends same color as Tube) su BrickScout
LEGO 4526985 TUBE W/DOUBLE Ø4.85 - MEDIUM STONE GREY
Lego TUBE, W/ DOUBLE 4.85 HOLE (Design 29219) - Choose Part number (Colour) | eBay
Tubes 45026 | LEGO® Education | Buy online at the Official LEGO® Shop US
Lego® Technic 25214, 38896, 6176298 tube elbow, axle hole, red
Hose, Ribbed 7mm D. 11L / 8.8cm : Part 78c11 | BrickLink
Lego 1x1 Brick Round Tube Column Pick Color Black Gray Trans Blue Yellow NEW X20 | eBay
Lego Technic Bricks 6x Medium Stone Grey Elbow 90deg Tube 25214 6151349 NEW | eBay
The new macaroni tube | Brickset
LEGO® 621130 - 4540890 73590c02a - ToyPro
LEGO PART 25214 Brick Round 1 x 1 diameter Tube with 90 Degree Elbow (2 x 2 x 1) and Axle Holes (Crossholes) at each end | Rebrickable - Build with LEGO
75535 Tube ?7.84X16 - Swooshable
LEGO Duplo - Ball Tube Holder 42029 Red - DECOTOYS
Technic Tube - Flexible - LEGO® Brand Hose Flexible 8.5L with Tabless Ends - The shop Briques Passion