Synthrapol requires hot water. For prewashing fabric, though, you might be better off using Retayne (which also requires hot water). Retayne sets dyes; Synthrapol suspends unset dyes in the water so they can be washed away (instead of settling into other fabrics as bleeds).
Be aware that front loaders do not use enough water for these products. If you have a front loader, you might want to use your kitchen sink and some rubber gloves (to agitate the fabrics) instead.