09-02-2016, 07:08 PM
That's a union, not a nipple. The nipple is the part you open to bleed the fluid through. 
You will be able to do it tight enough with molegrips, but if you're replacing other pipes might as well replace that while you're there.
You will be able to do it tight enough with molegrips, but if you're replacing other pipes might as well replace that while you're there.