Simply Koi and More Koi

hi i am in the start of changing to a RETRO FIT AIRATED BOTTOM DRAIN and the pump i want to use has 3 feet of lead i would like it longer and super watertight as the lead needs to go under water
has any one here done this
ps i am after the top part of the RETRO FIT AIRATED BOTTOM DRAIN as well as that bit is not with it

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you can buy an under water joint so you can join 2 cables together or if your local i can come over and change the wire on the pump for you