We use "Shmuffex" on yellow tubes with black moul;d spots. It takes a few applications, but it works. However, it has been out of stock at our suppliers for a while now - so good luck finding some. Direct bright sunlight is also good
I’ve had good results with Cillit Bang black mould remover.
I usually scrub the tubes first with diluted TFR and a slightly used green scouring pad, after rinsing I use the cillit bang with a different slightly used green pad [emoji1305]
We use "Shmuffex" on yellow tubes with black moul;d spots. It takes a few applications, but it works. However, it has been out of stock at our suppliers for a while now - so good luck finding some. Direct bright sunlight is also good