Step 1: Find the centre of the circle.
Since the two given lines are diameters of the circle, their point of intersection is the centre of the circle.
The equations are
\[
x+y=6
\]
and
\[
x+2y=4.
\]
Subtracting the first equation from the second,
\[
y=-2.
\]
Substituting in
\[
x+y=6,
\]
we get
\[
x-2=6.
\]
\[
x=8.
\]
So, the centre is
\[
(8,-2).
\]
Step 2: Find the radius.
The circle passes through
\[
(6,2).
\]
Therefore, the radius is the distance between \((8,-2)\) and \((6,2)\).
\[
r^2=(6-8)^2+(2+2)^2.
\]
\[
r^2=(-2)^2+4^2.
\]
\[
r^2=4+16=20.
\]
Step 3: Write the equation of the circle.
The equation of a circle with centre \((8,-2)\) and radius squared \(20\) is
\[
(x-8)^2+(y+2)^2=20.
\]
Expanding,
\[
x^2-16x+64+y^2+4y+4=20.
\]
\[
x^2+y^2-16x+4y+68-20=0.
\]
\[
x^2+y^2-16x+4y+48=0.
\]
Step 4: Final conclusion.
Therefore, the required equation is
\[
\boxed{x^2+y^2-16x+4y+48=0}
\]